Two months after fire consumed a building in San Francisco’s Mission District, many owners of the more than 30 businesses that were displaced are still trying to figure out how to cope with the steep price of reestablishing themselves.

By 2005, when a federal judge lifted the most recent desegregation orders, San Francisco Unified School District had been trying for more than three decades to make its schools more racially and socioeconomically diverse, starting in 1971 with forced busing. San Francisco schools no longer exhibit the level of racial isolation they once did, but they are now resegregating, as are many others across the country. In 2013–2014, in more than one-quarter of city schools, 60 percent of the students were of one race. That is a far cry from 1966, when more than one-third of the schools had student populations with 80 percent or more belonging to a single racial group. (In 2014, just three schools were segregated to that degree.)

Each January, parents across San Francisco rank their preferences for public schools. By June, most get their children into their first choices, and almost three-quarters get one of their choices. A majority of families may be satisfied with the outcome, but the student assignment system is failing to meet its No. 1 goal, which the San Francisco Unified School District has struggled to achieve since the 1960s: classroom diversity. Since 2010, the year before the current policy went into effect, the number of San Francisco’s 115 public schools dominated by one race has climbed significantly.

Over five decades, San Francisco saw a demographic transformation in its public school system. In 1969, white and black students together were the majority, as in most of the rest of the United States. Since then, San Francisco public school enrollment has fallen by 39 percent, and almost all the missing faces are white or black. But the two groups have not disappeared in the same way.

If one looks at the San Francisco Unified School District as a whole, a clear pattern emerges: Schools with the highest level of achievement tend to have the lowest levels of family poverty. And schools that are identified as “racially isolated” are visibly clustered by both income and achievement. This plot shows the base Academic Performance Index for each school in the district for which data are available, as well as the percentage of students poor enough to qualify for free and reduced-price lunches, which are used as a proxy for measuring poverty.

Schools across San Francisco show markedly different levels of racial and ethnic diversity. Increasingly over the last five years, schools are dominated by one racial group. With mathematical tools, it is possible to measure which schools are the most and least diverse. We chose to rank schools using a formula that economists use to tell whether an industry is dominated by monopoly ownership, the Herfindahl-Hirschman index, also known to ecologists as the Simpson diversity index. The idea is the same: Sum up the squares of all the fractions of your sample. The higher the number, the lower the diversity.

While San Francisco’s school assignment system has benefited families with the means to transport their children to schools with the most desirable programs, it creates dilemmas for more disadvantaged students who must travel long distances to school, often without the help of their parents. Many lower-income students must choose between long commutes on unreliable public transit and attending lower-performing schools closer to home. This may help explain why San Francisco public schools, like those in many cities nationwide, are increasingly resegregating as decades of court-ordered diversity measures recede into history.

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